A wide variety of polyacrylonitrile fibers have been spun that possess certain desirable physical properties such as high strength, high wet melting point, and good resistance to shrinkage at elevated temperatures. These properties of polyacrylonitrile fibers facilitate their use in many commercial and textile applications. However, the use of polyacrylonitrile fibers was limited because these fibers did not possess sufficient flame retardant properties.
In an effort to increase flame retardant properties of acrylonitrile fibers, acrylonitrile has been copolymerized with certain monomers such as vinyl chloride and vinylidene chloride. The degree of improvement in this property varies with the type and amount of modifier copolymerized with the acrylonitrile. However, it was difficult to provide acrylonitrile fibers with such a modifier that provides adequate flame retardant properties while also providing acceptable fiber properties such as acceptable color, high resistance to shrinkage, high strength, high wet melting point, and acceptable dyeability. These difficulties are encountered, in part, due to the difficulty of solubilizing vinyl chloride or vinylidene chloride.
Various acrylonitrile copolymer blends were developed that included acrylonitrile and vinylidene chloride. For example, U.S. Pat. No. 2,769,793, which is incorporated by reference herein, describes an acrylonitrile copolymer blend, containing 85 percent or greater acrylonitrile polymer, that may include a variety of monomeric components such as vinyl chloride, vinyl acetate, vinylidene chloride and the like. The blend may also contain a dye-receptive monomer. U.S. Pat. No. 3,828,014, which is incorporated by reference herein, relates to fibers formed from a copolymer of acrylonitrile and one or more copolymerizable monoolefinically unsaturated monomers. However, these patents describe acrylonitrile blends that do not provide adequate fiber properties, fiber processability, fire ignition resistance, and dyeability at the same time.
The fiber industry strives to provide fibers that not only possessed flame retardant properties, but also provide improved fiber lightfastness, fiber dyeability and fiber color. U.S. Pat. No. 3,824,222, which is incorporated by reference herein, describes a flameproof acrylic fiber that contains acrylonitrile, vinylidene chloride and vinyl phosphonate. U.S. Pat. No. 3,974,130, which is incorporated by reference herein, relates to a non-flammable acrylonitrile-vinylidene chloride copolymer fiber that includes comonomers that have a special affinity for dyes. However, these fiber compositions, designated as modacrylic, contain large quantities of vinylidene chloride (i.e., in concentrations above 25% by weight). Prior art compositions with vinylidene chloride suffered from poor fiber characteristics and bad color. For fiber forming purposes, vinylidene chloride in quantities necessary to impart flame resistance can impart several undesirable properties to the fibers.
Satisfactory prior art copolymers were not obtainable when the vinylidene chloride content exceeds 25% by weight of the copolymer composition due to poor flame retardancy or poor base copolymer whiteness. Vinylidene chloride also adversely affects the lightfastness of the fiber as well as other properties such as UV resistance. Such large concentrations of vinylidene chloride in the prior art copolymers increase processing complications due to the low solubility of vinylidene chloride, and result in fibers that possess unacceptable properties such as insufficient fiber structure (e.g., tensile properties), lightfastness and dyeability.
One satisfactory modacrylic blend manufactured commercially was a combination of vinyl bromide and vinylidene chloride with other comonomers. One such blend contained 61.45 percent acrylonitrile, 1.5 percent sodium p-sulfophenyl methallyl ether, 12.5 percent vinyl bromide, 23.9 percent vinylidene chloride, and 0.65 percent styrene. This copolymer composition has the Chemical Abstracts number CAS #31532-91-9, which is an acrylonitrile-vinyl bromide-vinylidene chloride copolymer.
However, the availability of vinyl bromide has recently declined.
Accordingly, there is a need for modacrylic fiber compositions that provide fibers with the combined properties of desirable fiber structure, lightfastness, color and flame retardancy.
Moreover, there is a need in various other industries for fire retardant polymeric materials that may be formed into various products without encountering color complications inherent with prior monomer and copolymer compositions.